The present invention relates to a technique of forming a circuit and wiring in which a superconductive material is used and particularly to a process suited for forming a three-dimensional integrated circuit and wiring.
In the conventional thin film multi-layered substrate process using Cu-polyimide, a polyimide resin is used for the purpose of interlayer insulation. The patterning of the polyimide film is conducted by applying a polyimide resin solution, drying the resulting coating to remove the solvent, forming a resist layer, and conducting etching with an organic solvent. The patterned polyimide film is one prepared by heating to conduct exocondensation of the imide ring and therefore cannot be etched any more with an organic solvent. For this reason, the patterning of the second and subsequent layers each made of polyimide with a solvent brings about no damage to the polyimide constituting the lower layers. It is a matter of course that Cu which is a conductor is not damaged during this process.
On the other hand, in a thin film multi-layered wiring board in which a superconductive material is used as the conductor, annealing should be conducted at 400.degree. C. or above in an oxygen atmosphere after the formation of a film in order to convert the conductive portion into a superconductive material, which makes it impossible to use polyimide as the insulation film. The use of an inorganic oxide as the insulating film is considered as an expedient for overcoming this drawback. However, when an inorganic material is used, an acid, an alkali, or the like should be used in etching, which unfavorably brings about a drawback that the etching of the second and subsequent insulation layers causes a damage to the wiring layer and insulation layer provided thereunder.
With respect to prior art, Cu-polyimide multi-layered wiring is described in Nikkei Electronics published by Nikkei-McGraw-Hill Co., June 17, 243-266 (1985). Further, Japanese Journal of Applied Physics, Vol. 26, No. 5, p.p. L709-L710 and p.p. L738-L740 describes the preparation of a superconductive thin oxide film.
In the above-described prior art, no consideration is given to the formation of a multi-layered wiring board in which a superconductive material is used as the wiring conductor. This brought about a problem that the etching of the second and subsequent insulation layers caused a damage to the insulation layer and wiring layer provided thereunder.